The first coronavirus reported from the rabbit (RbCV) and the first coronavirus associated with cardiomyopathy in any species has been previously described by the PI. Pleural effusion disease (PED) described by Danish workers is thought to be caused by the same virus. From serum containing virus supplied by the Danish workers a pool of serum containing 100,000 rabbit infectious units (RIU) of PED virus per ml and antiserum to PED virus has been prepared. In an in vivo neutralization test PED antiserum neutralized both PED virus (100,000 RIU) and RbCV virus (10 million RIU); however, in a single trail RbCV antiserum neutralized RbCV virus (10 million RIU) but not PED virus (100,000 RIU). Additional trials using RbCV antiserum (from the same lot and a different lot of antiserum) and PED virus will be done. The results thus far indicate similarity between the 2 viruses. The one way neutralization most likely represents differences in potency of antiserum rather than major differences between the virus. The clinical course of the disease and the gross and microscopic lesions appear similar in the 2 groups of rabbits. In a separate study neither virus produced observable effects in nude mice or CD-1 mice and no antibodies were demonstrated against mouse hepatitis virus (a coronavirus) using the ELISA test. Hearts from acutely infected and recovered rabbits have been examined in vitro to assess physiologic function. Preliminary results suggest long term cardiac dysfunction following infection. This work is continuing and a time course experiment is planned in which hearts will be examined throughout the acute phase of the infection (through 12 days) and during the recovery period (more than 12 days). In conjunction with this work, infected rabbits will be studied for changes in their electrocardiograms and clinical chemical indices, usually related to changes in myocardial tissues, will be measured.